1. Field of the Invention
The present invention relates to a network node apparatus such as a packet transmission node, a packet transfer node, and a packet reception node, and a connections set-up method suitable for internetworking.
2. Description of the Background Art
In recent years, as indicated by the Internet Draft (draft-ietf-ipatm-frameworkdoc-06.txt and draft-katsube-router-atm-overview-01.txt), the techniques described in 1) and 2) below have been proposed.
These techniques provide methods of implementing a cut-through connection in a large scale switched network.
A connection whereby packet transfer without network-layer processing can be effected inside a logical network (e.g. IP subnet) is called a datalink connection. A connection constituted by linking a plurality of datalink connections at the network layer for inter-network communication is called a “hop-by-hop” connection. In a hop-by-hop connection, the network layer processing is performed by routers located at subnet boundaries.
In contrast, in a “cut-through” connection, the network-layer processing is bypassed by some means, even if the hop-by-hop packet transfer would conventionally be necessary. In other words, in the cut-through connection, packet transfer from one logical network to another logical network can be performed solely by processing at a lower layer than the network layer.
1) Next Hop Resolution Protocol (hereinafter abbreviated to NHRP): when a packet transmission node which belongs to one logical network interrogates a server about a network address of a destination node which belongs to another logical network, the server returns the link address of the destination node or the nearest router to the destination node. Then, a datalink connection from the transmission node to the destination node or the router nearest the destination is established based on this link address. This datalink connection is a cut-through connection.
2) Cell switch router (hereinafter abbreviated to CSR): for specified traffic, packet transfer is performed using only information of the datalink layer, bypassing the network layer processing in an intermediate router. This is implemented as follows. The intermediate router stores the correspondence relationship between a datalink connection belonging to one logical network and another datalink connection belonging to another logical network for the specified packet flow, and transfers packets using this correspondence relationship. As a result, a cut-through connection is formed.
Such cut-through connections can achieve high throughput and low latency packet transfer for internetwork environment.
However, in NHRP, normally every packet to be transmitted is a trigger for setting up a cut-through connection. Specifically, when a node intends to transmit a packet to an address for the first time, a cut-through connection is set up by resolving the address; after that, all packets having the same destination network address are transferred through this cut-through connection. Consequently, a cut-through connection will be established even when the improvement in throughput achieved by the cut-through connection does not in fact outweigh the overhead involved in setting up the cut-through connection. Furthermore, it becomes difficult to utilize the bandwidth of the communication channel efficiently because the cut-through connections which are not in fact much used occupies the bandwidth.
In contrast, for the set-up of a cut-through connection under CSR, apart from using every packet transmission as the trigger, is possible to use as the trigger a) the fact that more than a fixed number of packets have been transmitted to a given destination or b) the fact that a TCP (transmission control protocol) message in which the flag SYN is set is to be transmitted. However, in the case of a), the fact that it is necessary to count the number of packets for all destinations makes the node structure complicated, and besides, a cut-through connection cannot be set up until the number of packets has reached a certain value. And in the case of b), a cut-through connection will be set up even for traffic in which only small amounts of data are exchanged a small number of times (i.e. for traffic in respect of which benefit matching the overhead involved in setting up the cut-through connection is not obtained, and established cut-through connections unnecessarily hogs the communication channel bandwidth).